Rheumatoid arthritis (RA), an autoimmune inflammatory disorder, results in persistent synovitis with severe bone and cartilage destruction. Bisphosphonates (BPs) are often utilized in RA patients to reduce bone destruction and manage osteoporosis. However, BPs, especially at high doses, are associated with osteonecrosis of the jaw (ONJ). Here, utilizing previously published ONJ animal models, we are exploring interactions between RA and ONJ incidence and severity. DBA1/J mice were divided into four groups: control, zoledronic acid (ZA), collagen-induced arthritis (CIA), and CIA-ZA. Animals were pretreated with vehicle or ZA. Bovine collagen II emulsified in Freund's adjuvant was injected to induce arthritis (CIA) and the mandibular molar crowns were drilled to induce periapical disease. Vehicle or ZA treatment continued for 8 weeks. ONJ indices were measured by micro-CT (µCT) and histological examination of maxillae and mandibles. Arthritis development was assessed by visual scoring of paw swelling, and by µCT and histology of interphalangeal and knee joints. Maxillae and mandibles of control and CIA mice showed bone loss, periodontal ligament (PDL) space widening, lamina dura loss, and cortex thinning. ZA prevented these changes in both ZA and CIA-ZA groups. Epithelial to alveolar crest distance was increased in the control and CIA mice. This distance was preserved in ZA and CIA-ZA animals. Empty osteocytic lacunae and areas of osteonecrosis were present in ZA and CIA-ZA but more extensively in CIA-ZA animals, indicating more severe ONJ. CIA and CIA-ZA groups developed severe arthritis in the paws and knees. Interphalangeal and knee joints of CIA mice showed advanced bone destruction with cortical erosions and trabecular bone loss, and ZA treatment reduced these effects. Importantly, no osteonecrosis was noted adjacent to areas of articular inflammation in CIA-ZA mice. Our data suggest that ONJ burden was more pronounced in ZA treated CIA mice and that RA could be a risk factor for ONJ development. © 2016 American Society for Bone and Mineral Research.

Although osteonecrosis of the jaws (ONJ), a serious complication of antiresorptive medications, was reported a decade ago, the exact mechanisms of disease pathophysiology remain elusive. ONJ-like lesions can be induced in animals after antiresorptive treatment and experimental interventions such as tooth extraction or periapical or periodontal disease. However, experimental induction and manipulation of disease progression does not always reflect clinical reality. Interestingly, naturally occurring maxillofacial abscesses, inducing aggressive inflammation of the peri-radicular mucosa with significant osteolysis and alveolar bone expansion, have been reported in mice. Here, we aimed to explore whether osteonecrotic lesions would develop in areas of maxillary peri-radicular infections, in mice on antiresorptive medications with distinct pharmacologic action, thus establishing a novel ONJ animal model. Mice were treated with RANK-Fc or OPG-Fc that bind to RANKL or with the potent bisphosphonate zoledronic acid (ZA). Maxillae were assessed radiographically and histologically. μCT imaging of vehicle mice revealed several maxillae with altered alveolar bone morphology, significant ridge expansion and large lytic areas. However, in RANK-Fc, OPG-Fc and ZA treated animals the extent of bone loss was significantly less, but exuberant bone deposition was noted at the ridge periphery. BV and BV/TV were increased in the diseased site of antiresorptive vs. veh animals. Histologically, extensive inflammation, bone resorption and marginal gingival epithelium migration were seen in the diseased site of vehicle animals. Rank-Fc, OPG-Fc and ZA reduced alveolar bone loss, increased periosteal bone formation, and induced areas of osteonecrosis, and bone exposure that in many animals covered significant part of the alveolar bone. Collectively, our data demonstrate ONJ-like lesions at sites of maxillary peri-radicular infection, indistinguishable in mice treated with RAKL inhibitors vs. zoledronate. This novel mouse model of spontaneous ONJ supports a central role of osteoclast inhibition and infection/inflammation in ONJ pathogenesis and validates and complements existing animal models employing experimental interventions.